1. Field of the Invention
Typically, power trains for four wheel drive vehicles have a center differential for allowing front and rear drives to turn at different speeds when negotiating turns. Such a power train is well known from, for instance, Japanese Unexamined Patent Publication No.60(1985)-131,324. On the other hand, in order to mount a transmission in front engine, front drive vehicles and four wheel drive vehicles so that the transmission is properly received in an engine volume or room, it is typical to orient such a transmission and a transverse engine both in a transverse direction of the vehicle body and to place them side by side. The transmission is operationally connected to the transverse engine by a gear train or a chain. This arrangement results in reducing an overall length of the power train in a lengthwise direction of the vehicle body.
2. Description of Related Art
For improving the compactness of power trains, it is effective to use hollow shafts, disposed coaxially, as transmission input and output shafts so that it is possible to dispose a front drive shaft in the hollow input and output shafts. Such a construction is described in, for instance, Japanese Unexamined Patent Publication No.1(1989)-316,561. However, a coaxial arrangement of a front drive axle and input and output shafts causes a drawback in that these hollow input and output shafts and the front drive axle must be manufactured with high accuracy. Alternatively, arranging a front drive axle separately from transmission input and output shafts produces the following drawbacks:
(1) Installing a center differential in the output shaft of a transmission prevents the front drive axle from being positioned close to the transmission output shaft since a mechanical interference between the center differential and a front axle differential must be avoided. This prevents the power train from being constructed compactly. Additionally, the center differential, which is installed in the transmission output shaft, prevents the front axle differential from being located approximately centrally between front wheels.
(2) Installing a center differential and a front axle differential side by side in a front axle shaft makes the power train bulky in a transverse direction.
(3) Installing a center differential in a shaft, other than a transmission output shaft and a front drive axle, requires an increased number of power train parts.